Butylthiomethylene group

Although the n-butylthiomethylene group is subject to acid hydrolysis, basic conditions for hydrolysis have been developed and these seem to be preferred in actual practice. A typical procedure uses a mixture of a 25% aqueous potassium hydroxide solution with ethylene glycol heated at reflux. In this manner thioenol ether 101 was converted to 9-methyl-l-decalone (102) in 78% yield (equation 82). The rare use of acid hydrolysis is exemplified by the use of concentrated hydrochloric acid to hydrolyse the blocked lactone (104) to 105 (equation 83) . Additional examples of conversions using a thioenol ether intermediate are shown in Table 2. 

Advantages are claimed for the n-butylthiomethylene group which, because of the low conjugative ability of the second row sulphur atom, does not deactivate the system towards alkylation [124, 130]. Yields of alkylated cyc/o-hexanones are particularly good with this protecting group. 

Alkylation of ketones. 2-n-Butylthiomethylene-6-methylcyclohexanone allowed to react with methyl iodide in ferf-butanol in the presence of K-ferf-butoxide 2-n-butylthiomethylene-6,6-dimethylcyclohexanone (Y 84%) refluxed with KOH in aq. diethylene glycol -> 2,2-dimethylcyclohexanone (Y 77%).— The n-butylthiomethylene group does not deactivate the carbonyl and can be easily removed. F. e. s. R. E. Ireland and J. A. Marshall, Am. Soc. 81, 6336 (1959). 

An Illinois group has described a method of selective geminal alkylation of aaa -trisubstituted ketones the corresponding n-butylthiomethylene derivatives of such ketones undergo a process of double reduction with lithium in ammonia, affording a methyl-substituted enolate anion at the original methylene position, which can be alkylated in situ. This permits the introduction of a methyl group and a second, variable substituent at that ketone flank which condenses with ethyl formate (Scheme 81). 

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